Nanopore formation during electrolytic etching of silicon in hydrofluoric acid solutions

A stepwise scheme has been proposed for gaining insight into the nanopore formation process in silicon during electrolytic etching in hydrofluoric acid solutions. We have studied the influence of the concentration and nature of dopants (phosphorus, arsenic, and antimony) in silicon, current density, electric field strength, and etching time on the axial and radial pore sizes and the pore distribution density. The dopants have been shown to play a predominant role in the nanopore formation process. The shape and spatial orientation of nanopores in Si substrates with the (100) and (111) crystallographic orientations have been interpreted in terms of specific features of the electrochemical etching of silicon in hydrofluoric acid solutions, related to the action of the etching ion (HF2)(-). The observed discrepancy between the experimentally determined and calculated radial nanopore sizes has been accounted for by the low probability ( 6.25%) of simultaneous interaction of the fluorine atoms of an (HF2)(-) ion with the corresponding silicon atoms located at vertices of a cube of the crystal lattice.